The present invention relates to devices for infusing, administering, injecting, delivering or dispensing substances, and to methods of making and using such devices. More particularly, the present invention relates to a method for identifying a change in pressure in the liquid path of a microdosing device, to a use of the method, to a device for carrying out the method, to a microdosing device with the device, and to a use of the device and/or the microdosing device.
For the precision dosing of liquid substances in the microliter range, as is used in the pharmaceutical and chemical industries and in medicine for feeding liquid medicaments, for example insulin, into patients' bodies, it is of greatest importance that the desired dosage is as exact as possible and any unintentional interruption to the feed, as may arise due to an empty liquid reservoir or an occlusion in the liquid path, is discovered and eliminated immediately.
In the case of insulin pumps with spindle-driven delivery pistons, it is known from the prior art to monitor the driving torque or the supporting force of the spindle and to draw a conclusion about an occlusion in the liquid path from an increase in said variable. However, this type of monitoring is imprecise and unreliable, since a large number of disturbance variables, such as, for example, the friction between delivery piston and wall of the liquid reservoir, are virtually impossible to detect and eliminate.
A transition has therefore been made to measuring the fluid pressure in the liquid path by an element which is acted upon by the fluid and transmits the fluid pressure or changes under the fluid pressure to a sensor, mechanically coupled to the element, which determines the compressive force transmitted by the element or a movement of the same to calculate the fluid pressure. Since, in most cases, the element which is in contact with the fluid is designed as a disposable article for hygiene reasons, but the sensor, on cost grounds, has to be used more than once, the known microdosing devices currently have the disadvantage that the accuracy of the pressure measurement decisively depends on the quality of the mechanical coupling between the element, which is in contact with the fluid, and the sensor, as a result of which, while the disposable articles are justifiably tolerated in terms of cost, a relatively great variation in the accuracy from measurement to measurement arises.